This invention relates to image data compression and decompression and more particularly to the deletion of form (background) data from an image during data compression and the addition of form data to compressed image data during decompression.
The present invention utilizes data which is in contour form encoded in accordance with the apparatus described in U.S. Pat. No. 3,987,412, Ser. No. 535,453, entitled "A Method and Apparatus for Image Data Compression Utilizing Boundary Following of the Exterior and Interior Borders of Objects", by T. H. Morrin, filed 1/27/75, and issued Oct. 19, 1976. In that prior apparatus, a mechanism for compression and reconstruction of an arbitrary image is described. The image is encoded by object such that the compressed image is a list of objects. Image manipulation operations can therefore be done directly on compressed data. One such operation which is the subject of the present invention is form removal or the correlation of an image with a template. This information generally refers to fixed preprinted information; i.e., text, rulings, logos on a document; for example, an insurance company form or gas station credit card receipt. In addition to the form information the image contains variable data information; such as, name, address, billing amount, etc. In a compression process it is desirable to strip image data of all form information as it is necessary to store form information only once, since this information does not change from document to document. During a decompression operation, it is necessary to add the form information to the compressed image so that the resultant decompressed image contains all of the information in the original document.
In the prior art, stripping of forms is accomplished by optical means. The form information is printed in a special color. Selective detection during the scanning process filters out the special color printing and thus drops the form electronically.
The optical method has the disadvantage that documents must be preprinted using special inks and special scanners. Furthermore, form data cannot be stripped from the information on a document which is, for example, a copy of the printed document.